Forecast API Load Process

We are running MRP (not ASCP) on 12.1.3.  We would like to change our forecast load process (weekly buckets, 1000's of items, multiple orgs).  Current process: Each month, we create a file of all records (52 weeks/item), and run a request set to load through the API.  The request set loads the forecasts, and then creates an error file.  The load file contains records for the items from next month's start date forward through 52 weeks. The request set deletes all records in the forecast designator (I'm not sure if this is custom code, or standard code), then loads all records from the load file. We would like to discontinue re-loading of all records, leave current records there, and extend the forecast by a month, each month.  For example, at the beginning of the fiscal year, we would load the sales forecast, and then just extend it out each month. When doing this, we would like to: